1. Field of the Invention
This invention relates to a heat-developable color photosensitive element excellent in developability and in image-transferability and, more particularly, to a heat-developable color photosensitive element capable of preventing a color turbidity as well as maintaining a high color developing efficiency and suitable for producing a multicolor image because of its excellent dye-transferability.
2. Description of the Prior Art
Conventionally known color photographic processes having used photosensitive silver halides have been superior to the other color photographic processes, in photosensitivity, gradient, image-preservability and the like, and have therefore been most widely put in practical use. In these processes, however, there are numbers of problems such as that it takes time and trouble to process because wet-processes are applied to developing, bleaching, fixing and washing steps, for example, that fears are entertained that the human body would be hurt by processing chemicals, that there is a fear of contaminating a processing room and a working personnel by the processing chemicals, and that it takes trouble and cost to dispose of waste materials.
Accordingly, there is a demand for the developments of a color image forming method capable of using a dry process.
Heat-developable black-and-white photosensitive materials have been known since early times, which are characterized in that the materials and developed by heat. There are the descriptions thereof in, for example, Japanese Patent Examined Publication Nos. 4921/1968 and 4924/1968, in which the photosensitive materials comprising an organic acid silver salt, a silver halide and a developer are disclosed. In addition, quite a number of heat-developable color photosensitive materials have been known to which the described heat-developable black-and-white photosensitive materials have been applied.
There are the descriptions of the heat-developable photosensitive materials containing couplers for photographic use and color developing agents in, for example, U.S. Pat. Nos. 3,531,286, 3,761,270 and 3,764,328, and Research Disclosure Nos. 15108, 15127, 12044 and 16479, and the like; the descriptions of those using leuco dyes in U.S. Pat. No. 3,180,731 and Research Disclosure Nos. 13443 and 14347, and the like; the descriptions of those to which the silver dye bleaching processes are applied in U.S. Pat. No. 4,235,957, and Research Disclosure Nos. 14443, 14448, 15227, 15776, 18137 and 19419, and the like; and the description of the heat-bleaching processes for heat-developable photosensitive materials in U.S. Pat. Nos. 4,124,398, 4,124,387 and 4,123,273; respectively.
With those proposals relating to heat-developable color photosensitive materials, it is difficult or impossible at all, according to time and circumstances, to bleach or fix a black-and-white silver image formed simultaneously, and a wet-process is required to apply even if it should be possible to bleach or fix the image. Preferable merit is rarely to be found in those proposals because a sharp color image may hardly be obtained and a complicated after-treatment is required.
In the meantime, there are the disclosures of heat developable color photosensitive materials capable of transferring diffusible dyes having been released by a heat-development so as to obtain color images, in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 179840/1982, 186744/1982, 198458/1982, 207250/1982, 40551/1983 and 58543/1983, and in addition, in Japanese Patent Application Nos. 122596/1982 and 229649/1982 which were applied by the present inventors. These proposals are that a dye-donor substance having diffusible dyes in one and the same molecule releases the diffusible dyes through the heat-developing reaction with an organic acid silver salt and dyes are transferred to the image-receiving layer of the photosensitive material so that a color image may be obtained. This type of the photosensitive materials is hereinafter called "Dye-releasing type".
In the meanwhile, the proposals made by the present inventors disclosed in Japanese Patent Application Nos. 229671/1982, 33363/1983 and 33364/1983 are that a colorless or light-colored dye-donor substance reacts with the oxidant of a color developing agent which is produced through the heat-developing reaction of an organic acid silver salt to form heat-diffusible dyes and the diffusible dyes are transferred imagewise onto an image-receiving layer so that a color image may be obtained. This type is hereinafter called "Dye-forming type".
Even in these dye-releasing type, dye-forming type and the like, however, the developability and/or image transferability thereof are unsatisfactory and, in particular, both of the developability and the image-transferability cannot be satisfied at the same time when a photosensitive material is double- or multi- layered so as to obtain a multicolored image. To be more concrete, a color turbidity will cause, a color developing efficiently (i.e., a color releasing or forming efficiency to a unit amount of silver) will be lowered, or the transferability of a dye from a lower layer to the upper one will be unsatisfactory. Therefore, they have not yet attanined the level of practical use.
There is a demand for the developments of such a heat-developable color photosensitive element as those capable of preventing color turbidity, having a high color-developing efficiency and a high image-transferability of dyes, and obtaining a high image-density, and suitable for obtaining a multicolor image.
After having continued a series of studies on the technical problems as described above, the facts have come to the knowlege of the inventors that the binders in the photographic constituent layer of a photosensitive element has not only a great influence on the coating properties of the layer and the dispersibility or unmobility of a color-dye doner substance and the like, but also a great control power over the developability and image transferability thereof.
However, in most of the photographic materials comprising the conventionally known heat-developable color photosensitive elements and image-receiving elements, a color turbidity and the problems caused in a color developing efficiency, a high-density image and the like have been tried to solve by a dye releasing or forming technique applicable to a photosensitive element comprising a dye doner substance or the like, or by a dye receiving technique applicable to an image-receiving layer of an image-receiving element. On the contrary, such attempts as tried to solve the problems by the binders of a photosensitive element are few. For instance, the aforegiven Japanese Patent O.P.I. Publication Nos. 179840/1982 and 186744/1982 disclose the dye-releasing type in which hydrophobic polymer binders are used as the binders for photosensitive elements; and the aforegiven Japanese Patent O.P.I. Publication No. 207250 discloses that either hydrohilic polymers or hydrophobic ones may be used and lists up a number of examples thereof. As the particularly preferred examples of the hydrophobic polymers, polyvinyl butyral, polyvinyl acetate, ethyl cellulose, polymethyl methacrylate, and cellulose acetate butylate, may be given.
Nevertheless, after tring various experiments by the inventions, it was found that, even if such concrete examples given as the particularly preferred hydrophobic polymers are used as a binder, it was difficult to satisfy at the same time both of the developability and the image-transferability by which a color turbidity is prevented with keeping a high color-developing efficiency and a dye is endowed with a high image-transferability.